This system is generally supplied by a cryogenic pump and the liquid vaporized in the hairpin is sent toward the client when the air separation unit is stopped.
Thus, in FIG. 1, a vaporizer 4 can be seen which consists of a cylindrical vessel 7 and a hemispherical dome, the two being separated by a vertical plate 13 pierced with openings. These openings are linked to U-shaped pipes so that one end of the pipe is attached to an opening in the bottom part of the vertical plate 13 and the other end is attached to an opening in the top part of this plate. The dome is divided in a seal-tight manner into a top part 5 (i.e., exhaust chamber) and a bottom part 3 (i.e., intake chamber) by a horizontal planar plate forming a wall 6. A liquid to be vaporized 1 is introduced into the bottom part 3 which forms a supply chamber and circulates in U-shaped tubes 17. Some of the tube openings in the plate 13 are higher than others, so that the liquid reenters into the tubes at different levels. The liquid arrives toward the top part 5 of the dome 2 which constitutes an exhaust chamber. There, it is entirely vaporized by virtue of the heat exchange with steam 9 or other heat-generating gas sent into the vessel 7 and which circulates around the tube or tubes 17. The gas formed 15 by vaporizing the liquid is drawn from the top part 5 of the dome 2. The cooled steam 11 leaves into the atmosphere at the top of the vessel 7.
This vaporization system has a relatively lengthy start-up time; even when the cryogenic pump is sending the full flow rate toward this standby system, there is a wait of between 30 seconds and one minute before the full vaporization flow rate is observed.
This delay does not present a drawback in methods where a buffer vessel containing gas ensures the transitional flow rate between the shutdown of the unit and full production of the vaporization system. However, this type of buffer vessel is expensive, especially when the operating pressures are high.
A finer analysis of this response time shows a linear response of the production flow rate as a function of time on production ramp-up, but also on production ramp-down. From this curve, we can deduce that the response of the system is very strongly correlated to the liquid inertia of the bottom part 3. In practice, the production of the vaporizer will be maximum when all the tubes 17 are supplied, therefore when the supply shell 3 is filled with liquid.